Radio antennas are widely used in conjunction with various types of radio frequency transmitters and receivers. A variety of shapes and electrical configurations are employed, ranging from end-fed antennas which are substantially linear conductive rods of various lengths, having specific relationships to the wave lengths of the frequencies of the signals transmitted from or received by such antennas, to complex arrays of components. End-fed antennas are commonly used in mobile communications applications for radio telephone, ham radio, and CB (citizens band) applications. Because end-fed conductive rods (more commonly referred to as "whip" antennas) necessarily are quite long for the frequencies employed in mobile radio communications, attempts have been made to compact the overall antenna length at given wave lengths of signal frequencies by utilizing helical antennas or composite antennas involving combinations of various antenna shapes and configurations, such as complex lens antennas, multiple tuned antennas, dipoles and the like.
A problem which has been encountered in the past with the use of helical antennas in place of the more simple whip antennas is that short helical antennas, in theory and in practice, have exhibited considerably reduced efficiency compared with a conventional end-fed whip antenna. For example, for an antenna operating at the CB center frequency of 27 MHz, a three foot base-loaded helical antenna has 20% of the efficiency of a one-hundred two-inch whip antenna operating at that frequency. As a consequence, helical antennas have not proved popular with mobile communications users who are interested in obtaining maximum efficiency from their equipment. Thus in the past, mobile communications users, such as CB users, had to reach a compromise between antenna length (that is the long whip antennas) and lowered efficiency if a short antenna was desired or necessary.
In order to provide sufficient power, either for transmission or reception, for conventional antennas in any given situation, it often is necessary to have extremely large antenna structures or antenna towers to obtain the desired operating characteristics of the transmitter or receiver. Such structures are costly to build; and because of the substantial space they require or the substantial height to which they must reach, result in expensive, cumbersome and unattractive installations. For example, two-way radio antennas, such as are used for ham radio, CB radio base stations, and the like, require large unsightly installations if any reasonable range is to be obtained from the radio system using the antenna.
Therefore it is desirable to provide radio transmitting and receiving antennas of reduced length or height from those conventionally used and which exhibit little or no loss in efficiency when compared with long whip or end-fed rod antennas of the prior art.